Project Summary: The negative impact of obesity on physical function in older adults is largely unrecognized, yet close to 40% of older adults in the U.S. are obese and almost all have reduced physical function due to excess body fat plus age-related decline in muscle mass/strength (sarcopenia). Obesity is especially common in older African Americans, who as a result face greater functional decline and higher rates of Type 2 diabetes than whites. Obesity treatment can improve function and muscle health but it threatens long term functional outcomes due to concomitant loss of lean mass. Lowering of muscle mass is a concern not only for future functional status but it could also lead to impaired glucose tolerance. Unless effective interventions can be found to circumvent these challenges, the older adult physically limited by sarcopenia and excessive adiposity is likely to become the most common phenotype of geriatric frailty in the near future. The proposed study concerns a variety of important consequences of late life obesity but its primary focus is on the detrimental influences of obesity on physical function in older individuals who are at very high risk for frailty. Recognizing the high prevalence of Type 2 diabetes in older individuals (especially African Americans) and its links with poor muscle quality, the intervention will target men with prediabetes and assess their changes in insulin sensitivity, as well as their functional responses, to the interventions. A novel (higher- protein, balanced by meal) weight loss regimen that has been previously shown to improve physical function in obese, frail older adults will be tested in obese older white and black Veterans with functional limitations. The intervention regimen will be culturally tailored to meet the individual preferences of the target population and adapted to make sure low-income participants are able to afford the healthy foods in their diet plan. A total of 168 obese (BMI ?30 kg/m2) male Veterans aged ?60 yrs, with mild to moderate functional impairments (Short Physical Performance Battery score of 4 to 10 units) and prediabetes, will be randomized to a higher-protein weight loss treatment or an RDA-level protein control weight loss treatment. All participants receive individualized calorie prescriptions calculated to achieve a weight loss of ~1-2 pounds per week and attend weekly group support sessions designed to enhance diet compliance with goal setting, self- monitoring, stress management, and daily diet journaling; [they will also attend a weekly low impact, chair exercise class]. Higher-protein group participants are provided a supply of chilled/frozen high quality protein foods (lean meats, low fat dairy products, eggs) sufficient to give ?30 g high quality protein for two of three meals daily to help assure diet compliance. Treatment responses will be compared for the primary outcome of functional performance by Short Physical Performance Battery and important secondary measures, including muscle quality, insulin sensitivity, lean body mass, [physical activity, recent falls and fear of falling], instrumental activities of daily living, and quality of life at 0, 3 and 6 months. An exploratory aim examines potential mediators of racial differences in treatment responses and documents the most successful intervention strategies. This will be the first randomized controlled trial of a balanced, higher-protein diet during a metabolic challenge (caloric restriction) in those with prediabetes and the first study to look at racial differences in responses of obese older men to this regimen. Study findings will [fulfill the RR&D mission by advancing interventions to improve physical function in older Veterans], yield novel information about the impact of balanced, higher protein on muscle quality and insulin sensitivity, and explore racial differences in responses to obesity interventions.